That's what Dutch researchers report after following nearly 500 teens for five years, starting at age 13.

"Mood swings are greatest in early adolescence," said Dominique Maciejewski, a doctoral student at VU University Amsterdam, who led the study. "Most teens get less moody across adolescence."

She advises parents to stay calm and patient, and not to panic. "Parents would be advised not to worry too much about their teenager's moodiness, as these will decline in most cases," Maciejewski said.

The study also found that although "girls show more mood swings in sadness and happiness, both boys and girls show similar changes in their mood swings across adolescence."

The researchers followed 474 Dutch teens, 40 percent of whom were considered at high risk of aggression or delinquency at age 12.

Each year, for three weeks of the school term, the kids rated their daily moods in terms of happiness, anger, sadness and anxiety.

The researchers looked at fluctuations in day-to-day mood and developmental changes over the five-year span. The results were published Oct. 14 in the journal Child Development.

Maciejewski can't say for sure if the findings would apply to U.S. children, but suspects they might.

Exactly what drives the ups and downs was not part of the study, but Maciejewski said a number of factors might explain them.

Hormonal or brain-related changes in early adolescence might have an influence, she said. "For instance, there are studies that indicate that cognitive control systems lag behind the development of emotional systems during that time, which makes adolescents hypervigilant to emotional cues but does not provide them with enough cognitive capacities to suppress their emotional reactions," she said.

Also, significant social factors coincide with puberty that may induce more fluctuations in negative and positive emotions, Maciejewski said. These include the transition to high school, conflicts with parents (curfews are one example), greater peer affiliation, or first romantic relationships. "Additionally, during that time, they are still learning how to cope with their emotions," she said.

Gilda Moreno, a clinical psychologist at Nicklaus Children's Hospital in Miami, believes some of the moodiness is driven by a teen's temperament. "People are born with personality and temperament," she said, noting some teens are naturally calmer than others.

While the Dutch researchers found more variability in the happiness and sadness reported among girls than boys, that might reflect girls' greater tendency, in general, to express their feelings, Moreno said. "Boys might have had the same ups and downs, but not talked about it as much," she speculated.

Parents can employ a number of strategies to stay sane through the ups and downs of adolescence, Moreno said. For instance, if your teen is rude and disrespectful, she advised stepping away and avoiding conversation, explaining why. Say something like: "I can't talk to you right now. You are being disrespectful," she said.

Once everyone has calmed down, you can have a productive conversation, Moreno said. If moodiness centers on sadness or depression, parents should listen and gauge how seriously upset the teen is.

Maciejewski agreed. "It is best to listen carefully to their expressions of anger, fear and disappointment," she said. "Staying in touch by exchanging and discussing experiences will help their teen not to drift away from contact with the parent, and at the same time help the teen to quietly think about the reasons and solutions for their mood changes."

Sometimes it helps to offer alternative interpretations of events, "but only if the teen wants to listen to these," Maciejewski said. "Only when mood swings stay high in late adolescence, professional help may be needed," she said.